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Nine Men's Morris is a duel of mills: line up three of your pieces along any marked line and you get to pluck one of your opponent's pieces off the board. The catch is that the game changes character three times. First you both drop your nine pieces onto the 24 intersections, fighting for the well-connected crossings where two mills meet. Then you grind through the movement phase, sliding along the lines to open and re-close mills. Finally, when someone is whittled down to three pieces, those survivors gain the power to "fly" anywhere, turning a losing position into a knife-fight. Outlast your rival to two pieces, or freeze them with no legal move, and the win is yours.
How to Play Nine Men's Morris
The board is three concentric squares joined by lines at the midpoints of their sides, giving 24 intersection points. Each player gets nine pieces. In the placement phase you take turns dropping one piece on any empty intersection until all 18 pieces are down. Whenever you complete a mill — three of your own pieces on one of the board's straight lines — you immediately remove one of the opponent's pieces. Only orthogonal lines count as mills here; there are no diagonal mills, so the board has exactly 16 mills (eight horizontal, eight vertical).
Once every piece is placed, the movement phase begins: on your turn you slide one piece along a line to an adjacent empty point. You cannot jump over pieces or hop to a non-connected point. Forming a fresh mill on the move again lets you capture one enemy piece. When you remove a piece you must take one that is NOT currently part of a mill, unless every opponent piece is locked inside a mill — only then may you take one from a mill.
When a player is reduced to exactly three pieces, those pieces enter the flying phase and may move to any empty intersection regardless of adjacency. You win in one of two ways: reduce the opponent to two pieces (they can no longer form a mill), or leave them with no legal move on their turn. The reduce-to-two win is only triggered once the player being reduced has finished placing all nine of their pieces, so captures during the early placement phase never end the game outright.
Mill Tactics: Crossings, Swing Mills, and the Three-Piece Endgame
During placement, fight for the four cross points at the middle of each side (the T-junctions where the connecting spokes meet). Every point on this board sits on exactly two mills — corners included — so a crossing is not worth more because it 'feeds more lines.' It is worth more because it has four connections instead of two: those four points give you the most mobility and act as the hub where two mills physically cross, which is exactly what you need to build a swing mill later. Spreading across several lines also forces your opponent to spend tempo blocking, and the AI's evaluation explicitly rewards both 'two-of-three' lines and raw mobility, so it will contest those same crossings. Try to seed two threats that share an empty point: the opponent can only block one.
The signature weapon is the swing mill (also called a running mill or double mill): two mills that share a piece, so moving that one piece back and forth completes a mill on every single turn and captures a piece each time. The four cross points are the natural anchors for one. Setting it up is usually decisive. The defensive mirror is just as important — recognize when your opponent is one slide away from a swing and occupy the empty pivot point before they can oscillate.
Open and reform: a mill you break this turn can be re-closed next turn for another capture, because the engine only checks whether your destination forms a mill — there is no rule against immediately rebuilding a mill you just dismantled. So don't be afraid to march a piece out and back in. When you capture, prefer removing a piece that is doing defensive work — one that blocks your own near-mill or anchors the opponent's mobility — rather than a random straggler. Mobility matters: a player with no legal move loses, so squeezing the opponent's pieces into dead ends is a real winning plan, especially against the lower difficulty levels.
Mind the flying phase. Reaching three pieces is not an automatic loss — those pieces can teleport anywhere, making it brutally hard for the opponent to set up an unblockable mill, since the flier can drop onto any threatened point. Conversely, if you are ahead, keep up a double threat the flier cannot cover with a single move. Against the hardest AI (Hard searches six plies deep with no random blunders) you need clean double threats; Easy plays a random move about 30% of the time and Medium about 10%, so patient mill-building will punish their occasional slips.
Frequently Asked Questions
Are there diagonal mills in this version of Nine Men's Morris?
No. This version uses only the 16 straight lines along the squares' sides — eight horizontal and eight vertical. Three pieces on a diagonal do not form a mill and do not let you capture. This matches the traditional ruleset; the diagonal-mill variant is a different game.
Can I capture an opponent's piece that is already inside a mill?
Normally no. When you complete a mill you must remove a piece that is NOT part of any of the opponent's mills. The only exception is when every one of the opponent's pieces sits inside a mill — then, and only then, you may remove one from a mill.
What is the 'flying' phase and when does it start?
When a player is reduced to exactly three pieces, those pieces gain the ability to fly: instead of sliding to an adjacent point, they may jump to any empty intersection on the board. It kicks in automatically at three pieces and gives the trailing player a real chance to fight back by reaching any threatened mill in one move.
Can captures during the placement phase win the game immediately?
No. You can form mills and remove enemy pieces while placing, but the 'reduced to two pieces' loss is only checked once the player being reduced has finished placing all nine of their pieces. So losing pieces early in placement never ends the game on the spot — play continues until that condition (or a no-legal-move position) is reached after placement is done.
Are all 24 points equally valuable, and can the game end in a draw?
Every point lies on exactly two mills, so no point belongs to 'more lines' than another — but the four side-midpoint crossings have four connections instead of two, giving far more mobility and serving as swing-mill hubs, which makes them the most valuable squares. As for draws: this implementation never declares one. The game always resolves to a win — either someone is reduced below three pieces (after placing all nine) or someone is left with no legal move.